(1) Field of the Invention
This invention relates generally to composite materials which move in response to environmental changes, such as changes in temperature, and more specifically to a composite material installed as part of a propeller blade which is capable of changing its shape upon being heated.
(2) Description of the Prior Art
The basic objective of the present invention is to optimize the operation of a propeller for various angles of attack. A propeller blade is an airfoil that operates at a fixed angle of attack. The angle of attack of a fixed airfoil is only optimal at a single forward speed or a single rotation speed for a propeller. The drop off in efficiency is significant for the off design operation of the propeller. Prior art means of controlling propeller blade or wing angle of attack such as flaps or other articulated devices that rely on moving parts are prone to problems associated with wear, control and generation of noise.
In this regard, variable camber blades are well-known in the art. Reference can be made to U.S. Pat. No. 3,042,371 to Fanti and U.S. Pat. No. 4,619,580 to Snyder as representative prior art in this field. The patent to Fanti discloses a blade having a trailing end portion with upper and lower bimetallic sheets that changes the blade's shape upon being subjected to varying temperatures of the fluid through which it is operating. Snyder shows a variable camber vane that is also capable of changing its overall shape upon being subjected to thermal variations of its working fluid.
A significant shortcoming with the blades of Fanti and Snyder is that they change shape only when the fluid in which they are operating changes its temperature. Thus, there is no independent means for changing the shape of the blade apart from varying the temperature of the working fluid. In operation of a vehicle, it is impractical to change the temperature of the working fluid.
Reference can also be made to U.S. Pat. No. 5,114,104 to Cincotta et al. which discloses a fin having a mechanically controlled system for changing its shape. The system incorporates shape memory alloys which are embedded within the fin for changing its shape during use. A disadvantage associated with this design is that it is costly to manufacture since the design requires several expensive moving parts and additional labor costs.
There is presently a need for a propeller blade mechanism that is capable of changing the shape of the blade by a simpler, more reliable means.